1. Field of the Invention
The present invention relates to a sheet supplying apparatus used in an image reading apparatus such as a copying machine and the like.
2. Related Background Art
Conventional automatic original supplying apparatuses can be divided into two types an original circulating type (RDF), and a non-circulating type (ADF). In the apparatuses of original circulating type (RDF), exposure is completed while an original being conveyed is passing through an exposure portion, and a discharge device on which the exposed originals are discharged is provided above (or below) an original resting portion, and, even when a plural number of parts are handled, such handling can be performed by re-circulating the originals successively.
Since a combination of a flow reading mode (in which the exposure is completed while the original is being shifted) and the original circulating type (RDF) can reduce "loss time" by the time corresponding to the shifting time period of the exposure device in comparison with a stationary or fixed reading mode (in which the exposure device is shifted along an area of the original after the original is once stopped), a time period for exchanging originals can be reduced, and high speed and high productivity in the copying system can be achieved. Further, in comparing a predetermined original exchanging time period, in the combination, it is evident that the originals can be circulated at lower shifting speed than the stationary mode, thereby reducing noise.
As an example of the combination of the flowing mode and the original circulating type (RDF), there is a system in which high speed and high productivity in the copying system can be achieved by using a flash exposure technique. In comparison with the above-mentioned exposure device, since the flash exposure technique is designed to expose the entire surface of the original simultaneously, a high power light source and a belt-type photosensitive member are required, thereby making the whole apparatus bulky and expensive and increasing power consumption. Thus, this technique has been adopted by only some of large and high speed apparatuses.
On the other hand, in the original supplying apparatuses of non-circulating type (ADF), the original is fixed to a predetermined position on a platen, and the exposure operations corresponding to the number of copies are repeated by reciprocally shifting the exposure device. After the exposure operations are finished, the original is discharged onto a predetermined discharge tray. By repeating such operations regarding the remaining originals successively, the plural number of copies for plural originals can be obtained. In this regard, as the copying system, since the originals are not required to be circulated repeatedly by combining with a sorter at an output side, the damage of the originals can be reduced.
Among the above-mentioned various conventional techniques, there have been proposed various techniques for achieving the high speed operation and reduction of noise. As an example, as shown in FIG. 13, there has been proposed an image reading apparatus in which originals P, resting on an original stacking plate 302, are automatically supplied by either of two sheet supply rollers 312, 313, provided on both ends of the original resting plate 302, in dependence upon the size of the original P or/and a selected mode. The supplied original is sent to a predetermined position on a platen 105 to which an image reading portion 311 of a copying machine 301 is opposed and at which an image on the original is read.
The apparatus shown in FIG. 13 includes a system capable of re-circulating the originals P. In the original stationary reading mode (mode in which the original is supplied by the sheet supply roller 312), the plural originals P resting on the original resting plate 302 are separated one by one by means of a retard belt 5a and a supply roller 5b (first separation/supply means), and the separated original is sent to the predetermined position on the platen 105 by a convey belt 315 through a path 314. After the image is read by shifting the image reading portion (optical system) 311 in the copying machine 301 in a direction shown by the arrow e in FIG. 13, the original P is directed into a discharge path 316 by reversely rotating the convey belt 315 and then is discharged onto the original resting plate 302 by discharge rollers 303.
When the flowing reading mode is selected, for example, originals having a small size (for example, A4 size, B5 size or LTR (letter) size) are stacked on the original resting plate 302. When a start key (not shown) of the copying machine 301 is turned ON, in a condition that an inlet sensor 307 is ON and an original length detect sensor 310 is OFF, the flow mode is started. First of all, the original resting plate 302 is rotated around a fulcrum 309 to be lowered to a predetermined position, where an original bundle (original stack) P is bundle-conveyed by a stopper (original bundle convey means) 306 toward a second separation belt 304 until the original bundle is detected by a bundle convey position detect sensor 308. Thereafter, the originals P are separated and supplied one-by-one by means of the separation belt 304 and a supply roller 305. When the original is sent onto the platen 105 by the convey belt 315 through a path 317, the image on the original P is read by the original flowing reading mode, and, thereafter, the original P is directed into the discharge path 316 and is discharged onto the original resting plate 302 by the discharge rollers 303.
Whenever the original P is discharged onto the original resting plate 302, a trail end of the original P is pushed by the stopper 306 toward the second separation belt 304, thereby improving registration between the originals. Thus, if the originals are circulated again, since the trail ends of all of the originals abuts against the stopper 306 after all of the originals P were discharged on the original resting plate 302, the originals can be bundle-conveyed collectively by the stopper 306 to effect re-supply of the originals.
On the other hand, in the original supplying apparatuses of non-circulating type (ADF), as shown in FIG. 14, when the original P is supplied onto the platen 105, the exposure device is fixed at a predetermined position below the platen 105. Then, the flow reading mode is effected. After the flow reading mode is finished, the original is discharged onto the discharge tray. However, if a plural number of copies are desired, after the flow reading mode is finished, the original P is not discharged, but, the original P is stopped temporarily at that position where the flow reading mode is finished. Thereafter, the image reading is effected by reciprocally shifting the exposure device by times corresponding to the predetermined number of copies, to then discharge the original onto the discharge tray. In this way, the plural number of copies can be obtained by the combination of the flowing mode and the stationary mode.
However, for example, in case of the apparatus shown in FIG. 13, since the apparatus is of the original circulating type, in the flowing mode, the high original exchanging speed can be obtained and high productivity can be achieved, so that, as mentioned above, noise can be suppressed. However, if plural number of copies are desired, each original must be circulated by times corresponding to the parts of copies, with the result that the original being passed through the separation means is subjected to stress and curl is generated in the original being passed through the curved path. Thus, the original P is greatly damaged, and, poor conveyance of the original during the handling of the original frequently occurs, thereby not achieving high reliability.
On the other hand, in case of the apparatus shown in FIG. 14, since the originals P are not re-circulated, although the damage of the originals can be reduced, there arise many problems in consideration of the high original exchanging speed and high accuracy for registration between the original P and a recording sheet on which the image is to be formed. For example, although the flow reading positions are defined at 401 or 402, for example, if the original having a small size is handled by the flow reading mode, in a copy mode having a 1:1 ratio, so long as an original-to-original distance is kept constant, predetermined productivity (processing efficiency) can be achieved. However, in a copy mode having 1:N (plural) ratio, since a distance lx from an image tip end timing sensor 403 to the flow reading position 401 is long, the original exchanging time period becomes great.
That is to say, when the combination of the flow reading mode and the stationary reading mode is effected, since the convey belt 404 cannot be shifted while a preceding original P is being read by the original stationary reading mode by shifting the optical system, a tip end of a succeeding original P must be waiting at a position at an upstream side in an original supplying direction (referred to merely as "upstream side" hereinafter) of the image tip end timing sensor 403. Thus, the original interval becomes great, with the result that the original exchanging time period is increased and high productivity cannot be achieved.
If the distance lx from the image tip end timing sensor 403 to the flow reading position 401 is shortened to improve the productivity, during the flow reading scan, the trail end of the original P will be subjected to shock due to the ON/OFF operation of a clutch of a separation/supply drive system provided at an upstream side, thereby distorting the image. As a result, the image reading reliability is worsened, or an image on a large sized original cannot be read, thereby providing an insufficient copying system.
To eliminate the above-mentioned drawbacks, there has been proposed an apparatus in which the damage of the originals is prevented, the noise of the apparatus is suppressed and high productivity can be achieved by combining the flow reading mode and the stationary reading mode. In this apparatus, by permitting scanning with the combination of the flow reading mode and the stationary reading mode, the scanning of the succeeding original P with the flow reading mode can be effected during the exchanging of the originals, with the result that the originals can be exchanged at a speed similar to an image forming process speed of about 500 [mm/sec] without increasing the original exchanging speed (although the originals are normally exchanged at a linear speed TOP of about 1300 [mm/sec]).
Further, since the productivity required for the original reading can be obtained, the reliability for reducing the noise and preventing the damage of the original P can be improved while maintaining high productivity. Further, since the image reading means and the original P are positioned in consideration of stop and rise-up control (minimum distance required for reaching the flow reading speed) of the original P to determine a positional relation between the flow reading image tip and the stationary reading image tip, and the flow reading is effected while keeping the distance between the preceding original P and the succeeding original P to permit continuous stationary reading, the reliability for achieving high productivity, reducing noise, and preventing the damage of original P can be improved.
In the above apparatus, as shown in FIG. 13, the known lower separation/supply system of a belt retard type, constituted by the retard belt 5a and the supply roller 5b, is used as the separation/supply means for the originals P. In this system, when the originals stacked in a face-up fashion are supplied from a lowermost one, there arises a problem that a rear surface of a second original P is rubbed by an imaged surface of a first original P to contaminate the rear surface. This problem has been solved more or less by proposing various countermeasures.
However, if sheets on which images were fixed in a poor manner are used as originals P and a large number of such sheets are stacked as an original bundle P, the above-mentioned contamination will become noticeable, and, thus, further improvement has been requested.
In consideration of the above, the inventors of this application have proposed an apparatus in which an air separation means is used as the separation/supply means disposed at the flow reading side which are normally utilized most frequently in the handling of the plural originals in order to improve productivity, as shown in FIG. 15. The air separation means has a separation air duct 23 having blowout nozzles 25 out of which air flows for floating the original bundle P, and a vacuum absorption belt 7 for air-absorbing and conveying a lowermost original P from the floating original bundle P.
In the above air supply system, by resting the originals on an original stacking tray 2 inclined upwardly toward the air separation means, it is necessary that double-feed of the originals is prevented and the trail ends of the originals are aligned with each other, by utilizing the weight of the original bundle P.
With this arrangement, an original bundle P including various originals having different sizes cannot be handled (however, in the apparatus shown in FIG. 15, since the conventional belt retard system is used at the stationary reading side, such an original bundle P including various originals having different sizes can be handled).
First of all, after the original bundle P is set on the original stacking tray 2 in the elevated position, when a copy button is depressed, the original stacking tray 2 is lowered to a flow reading permitting position and a recycle lever 3 is driven. The original stacking plate 2 is provided with an opening for preventing interference with the vacuum absorption belt 7.
Inside side regulating plates 4, there is disposed a detect means (not shown) for detecting a thickness of the original bundle P on the basis of a rotational angle of the recycle lever 3, and this detect means comprises a gear system for amplifying the rotational angle of the recycle lever 3, and a slit plate/photo-sensor for outputting the amplified rotational angle as a number of pulses (pulse number). When the recycle lever 3 is rested on the original bundle P, pulse signals corresponding to the thickness of the original bundle P are generated from the slit plate/photo-sensor of the detect means, which signals are sent to an MPU (microprocessor unit) for controlling the apparatus. In the MPU, the number of pulses is calculated, and, on the basis of a loop-up table (LUT) representing a relation between the number of pulses and a rotational amount of a separation air valve 24, a drive signal is sent from the MPU to a stepping motor for driving the separation air valve 24, thereby rotating the separation air valve 24 by a predetermined amount.
The LUT serves to control the device so that the rotational amount of the separation air valve 24 is controlled to increase a separation air blow amount in accordance with the thickness of the original bundle P as the thickness of the original bundle P is increased, i.e., to gradually increase the rotational amount of the separation air valve 24 from a completely closed condition to increase the separation air blow amount in proportion to the increase in the number of pulses corresponding to the thickness of the original bundle P, thereby separating the originals P effectively.
At the same time, a drive signal is sent from the MPU to a separation air fan motor, so that separation air, having a blow amount corresponding to the thickness of the original bundle, is blown against the original bundle P. Thereafter, the original bundle P is conveyed, by an abut shutter (first trail end regulating member) 41, to a position where the originals can be air-separated. When the original bundle P is conveyed, the vacuum absorption belt 7 is rotatingly driven at the speed same as a conveying speed of the original bundle P. In this way, the separation and supply of the original bundle P can surely be effected without destroying the original bundle.
However, in the aforementioned conventional example, although there is no problem when the size of the originals P to be used is predetermined, since the copying machine is normally designed so that originals P having various different sizes such as normal size, B5 size, A4 size, B4 size, A3 size and the like can be copied, the original supply for the next copying operation cannot sometimes be effected. The reason is that, for example, if the original stacking plate 2 is set to accommodate the largest original (having a maximum length (in an original conveying direction) among the above-mentioned sizes; i.e., A3 size original), for example, in the case where originals smaller than the A3 size original are used, when the originals are discharged onto the original stacking plate 2 again by discharge rollers 16 through a discharge path 19, the originals are stacked on the original stacking plate 2 in a non-aligned condition.
To avoid this, in the conventional technique, a rear wall of the original stacking plate 2 integral with the original discharge portion is shifted in accordance with the size of the original P to adjust the length of the original stacking plate 2 in the original conveying direction. However, since the original discharge opening is also shifted together with the rear wall, an independent drive system must be prepared for the original discharge portion or an arrangement capable of varying the distance of the convey path to the original discharge opening must be provided. Thus, the original discharge portion and the convey path to the original discharge portion are made bulky, thereby making the entire apparatus bulky.
Further, when the expansible/collapsible guide is used for varying the distance of the convey path, there is a great danger of jamming the original P at the junction of the guide, thereby worsening reliability. In addition, the original discharge opening must be shifted by the operator himself, and thus operability is also worsened.
Further, if the original discharge opening is shifted automatically in accordance with the size of the original P, since the apparatus becomes bulky and complicated, reliability is worsened.